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Imaging Los Angeles Basin via Directional Dependent Rayleigh Wave Ellipticity Using Data From the Lab2022 Nodal Array

Description: 

We deployed a temporary nodal array in the Los Angeles basin, comprising ~300 nodal geophone seismometers, composed of two dense lines (inter-station spacing of ~0.6 km) and a 2D distributed/shotgun array (spacing of ~2 km). We compute multi-component ambient-noise cross-correlations between all stations available in the area, including both regional broadband and nodal stations. We observe clear fundamental mode Rayleigh and Love waves in the period band of 1-10s, where higher mode Rayleigh waves are also observed for periods shorter than ~4s. We use array processing techniques to measure both surface wave phase velocity and Rayleigh wave ellipticity, or H/V (Horizontal-to-Vertical) amplitude ratios. The measured Rayleigh wave ellipticity clearly depicts the basin's lateral boundaries. Moreover, at each station, we examine the azimuthal dependency of the ellipticity measurements. We show that strong Rayleigh wave H/V azimuthal anisotropy is evident within the basin, which is potentially related to the stress-induced crack alignment. We compare our findings with the SCEC Community Velocity Model (CVM) and regional stress field model and discuss how the models can be further improved. As an accurate basin model is important to earthquake ground motion prediction, our newly acquired results demonstrate the utility of dense nodal arrays for shallow imaging in a densely populated urban setting for seismic hazard assessment.

Session: Anisotropy Across Scales - I

Type: Oral

Date: 5/3/2024

Presentation Time: 08:30 AM (local time)

Presenting Author: Konstantinos

Student Presenter: Yes

Invited Presentation: 

Authors